1. Field of the Invention
The present invention relates to joining two or more cartridges each containing different cell or tissue cultures in fluid connection.
2. Technical Background
The effect of an experimental drug or chemical in the human body is difficult to predict because of differences in blood composition, tissue binding, regional pH, and permeability of cell membranes. Ideally, a drug should enter the body, go directly to the diseased site while ignoring healthy tissue, do its job and then exit the body. Unfortunately, this rarely occurs since even if the drug is able to pass through the required membrane, it still may not reach its desired destination due to the fact that a drug, unless directly injected into the blood, must pass through a complex system of living cell membranes before it can enter the bloodstream. For example, chemicals that enter the digestive tract must be absorbed by the cells lining the small intestine and then transferred through the cell to the other side where the chemical can then be absorbed by the capillary cells into the blood stream. Many medications administered this way are never absorbed by the blood stream, because they are chewed up by the enzymes as they pass through the digestive system. If the drug does make it to the blood from the intestines, it may be broken down or altered by the liver. Factors such as these make it vital to understand how a drug will react to and affect certain parts of the body prior to use in the human body.
Initially, drugs were tested in Petri dishes, through modeling with computer programs, animal and humans testing, and despite this testing of many of these drugs, still have unforeseen side effects. This is because a drugs effect depends less on chemistry than on the way it navigates the obstacle course that encompass the human body. A drug often changes and evolves as it travels through the body, such as being broken down by the liver, absorbed by the intestines, or held onto by fat. Therefore, it is essential to monitor the progress of a drug as it moves through the organs and tissues, however it is difficult to rationalize conducting such preliminary tests on human subjects.
Currently methods of testing experimental drugs and chemicals include in vitro tissue and cell cultures; computer modeling of real-life situations used to make predictions about the toxicity of a substance and model the action of a drug in the body; and organs donated from organ donors artificially maintained for research purposes. Alternatively, and generally preferred for accuracy, is in vivo animal testing. Live animals are essential in research and testing because they reflect the dynamic interactions between the various cells, tissues and organs comprising the human body. Animal testing, however, poses obvious problems to researchers because it is an inaccurate model for human drug response. Also, the protests of animal rights activist groups are continuously pushing to ban animal testing all together. The number of animals needed for product safety development has been reduced greatly; however, many of the alternative means of testing are still in the development stage and cannot yet take the place of animal tests.
Recently, a cartridge has been developed in vitro that mimics the blood brain barrier (BBB) in vivo. The mammalian BBB is comprised of micro-vascular endothelial cells that act as a virtually impenetrable barrier, thus isolating the brain from systemic influences, while simultaneously providing a pathway for the transport of nourishment to neurons buried in the brain parenchyma. The selective permeability of the barrier plays a crucial role in regulating the trafficking that occurs between blood and the central nervous system. The cartridge grows endothelial cells in one or more hollow fibers contained in a sealed housing compartment. The endothelial cells are introduced to the hollow area of the fibers where they attach and grow. A pump regulates the flow of media that is introduced into the fiber, manipulating the amount pressure put on the cells. This method is unique because it grows the cells in the presence of chronic shear stress, or flow. This is an important factor in the development of endothelial cells; those cultured under chronic shear stress respond in a physiologic manner and form a monolayer, stop dividing, orient to the flow of medium and form tight junctions. Glial cells are then grown on the exterior of the fiber that secretes “permissive’ or “promoting” factors further influencing the proper development of the endothelial cells. This system provides an environment that is more realistic to that which occurs in vivo than other methods, such as endothelial cells cultured in standard culture flasks. In flasks, cells continuously grow and divide, never expressing tight junctions or other indicators of normal, in vivo physiology.
Thus far, this method has only been applied to the blood brain barrier. Each organ membrane has unique characteristics and transport requirements, therefore it is vital to have tests that will determine what drugs can and cannot enter certain organs, and how these drugs effect and are affected by the organs they contact. Tests using real human cells and tissues of these various organs have been limited however, due to the difficulties of developing procedures and techniques for growth, maintenance, and testing of these tissues and cells, and of devices and methods, which when these tissues and cells are incorporated, realistically mimic the respective organ.
It is an object of the present invention to grow cells and tissues from human organs in and/or about at least one hollow fiber and to test the effect of chemical compounds and agents on the cells and tissue. It is another object of the present invention to provide a system for joining several cartridges in fluid connection and testing the effect the cells and tissues have on the chemical compound or agent, and what portion of the chemical compound or agent passes through each cell or tissue culture. Finally, it is another object of the invention to describe a method of mimicking the body systems by joining several cartridges together in fluid connection, such that the chemical compound or agent passes through the contained cell and tissue cultures in the same order it would in the body. Therefore, the present invention provides a method for testing the course of a drug in vitro that will monitor and take into account the effect each cartridge containing different types of cells and/or tissue has on the drug.